Study On Composition Of Jarosite Crystal By Acidithiobacillus Ferrooxidans

Jarosite is the main secondary mineral which forms by oxidation of the metal sulfides under the acidic condition.It is a high performance, rare and expensive yellow inorganic pigment. Jarosite is a typical Environmental-Friendly Materials because it has good weather resistance, non-toxic and antacid characteristics. Fe²⁺ Can be rapidly oxidized to Fe³⁺ by Acidithiobacillus fermoxidans in the 9K liquid medium. A series of hydration reactions will occur in the solution, and a variety of multi-hydroxy complex ion will emerge in the solution. Ultimately the jarosite precipitation will produce in the solution.This paper is aimed to find the optimum synthesis conditions of jarosite by A. fermoxidans. In this research, concentrations of Fe²⁺, total Fe, and yield of jarosite precipitate were observed at the different initial pH values of 1.40,2.10,2.46,3.03,3.52,4.10,4.90,5.90, and different temperature of 25℃,30℃,35℃,40℃. The results show that the optimum conditions of jarosite synthesis are as follows: the initial pH value 4.1, temperature 30℃. Under the conditions, the output and yield of jarosite were 21.8g/L and 72.3%. L₉(3⁴) orthogonal experiment was designed with four factors of FeSO₄·7H₂O dosage (A), shaking speed (B), bacterial load (C) and reaction time (D), and two indexes of output and yield of jarosite. The results indicated: A3B2C3D3 was the best combination if using output as index; A₁B₂C₃D₃ was the best combination if using yield as index.The composition and structure of the typical precipitate which produced by A. ferrooxidans under the initial pH value of 4.10 and 2.46, the temperature of 30℃were identified by XRD, FTIR and XRF analysises. The results showed that the composition of the sample includes 89% of the jarosite and few hydronium jarosite and ammonium jarosite. The average particle size of jarosite samples was 6.563μm by laser particle size analysis. The jarosite samples at the initial pH values were 2.5 and 4.1 were observed by SEM. The results indicated that the latter jarosite particle size was smaller. To study the jarosite application in respect of pigment, the hiding power and matter soluble in water of jarosite samples at the initial pH values were 3.0 and 4.0 were detenninated. The results showed: that jarosite could be made a transparent pigment; matter soluble in water of jarosite samples at the initial pH values were 3.0 and 4.0 were 1.0% and 0.6% respectively.